The present invention relates to a posterior spinal system and method. In the prior art, posterior spinal systems are known. These systems include various appliances interconnected together to correct spinal column deformities.
In prior art systems, however, problems have developed, particularly as to the ability of the spinal rods to withstand the stresses placed thereon and as to the ability to mount various fixation appliances on the rods and maintain them in a desired position and orientation with respect thereto.
It has been found that modifications from a smooth surfaced rod, such as, for example, knurling or threading of the surface or providing ratchets along the rod, inherently result in weakening of the strength of the rod by creating stress risers for crack initiation on the outer surface of the rod. It is further noted, for example, that a knurled rod would need a larger diameter to provide comparable strength to a corresponding unknurled or smooth rod of smaller diameter.
Furthermore, it has been found that requiring a surgeon to pre-mount the various appliances on the rods, as may be required when threaded rods are used, is an inconvenient surgical technique, since if the surgeon miscalculates and needs to add or remove various appliances to or from the rods, complications in surgery result, since the surgeon must remove the rods from the patient after they have already been placed in situ for the purpose of unthreading or threading, appliances, therefrom or thereto.
As such, a need has developed for a posterior spinal system having rods of increased strength and having attachment means designed to be used to attach the various appliances on the rod without the need for pre-assembly prior to placement of the rod.
The following prior art is known to applicants:
U.S Pat. No. 4,202,644 to Soussloff discloses a mounting device designed to be used to mount a machine element on a rotary shaft. The device uses two interlocking split sleeves with the inner sleeve having a threaded end engaged by a threaded member coupled to the outer sleeve, with rotations of the threaded member causing movement of the sleeves with respect to one another which, due to their interface which includes conical surfaces, causes an increase in the diameter of the combined sleeves to cause a wedging of the shaft into an opening on the machine element. This is different from the teachings of the present invention wherein a locking sleeve assembly is provided which uses a single sleeve having a tapered outer surface and a threaded end and wherein a lock nut is threaded over the threaded end and has a flange to bear against a side surface of an element which is to be locked onto a smooth shaft inserted through the sleeve.
U.S Pat. No. 4,629,178 to Keene discloses an open back hook assembly for engaging a spinal column which includes the provision of a threaded rod to which respective sleeves and nuts are threadably mounted. Hooks are affixed to the rod by sliding them over the sleeves and tightening the respective nuts. This is different from the teachings of the present invention wherein the rods themselves are smooth throughout their lengths and connection of hooks or other fixation structures thereto is accomplished by wedging action between the hooks or other components with corresponding locking sleeve assemblies to secure them to the respective rod. Connector assemblies may be utilized between the rods. Thus, the present invention has advantageous aspects over and above the teachings of Keene by providing a smooth surfaced rod which is inherently stronger than a threaded rod, and by providing a locking sleeve assembly which allows easier placement and removal of hooks or other components therefrom.
U.S. Pat. No. 4,274,401 to Miskew discloses an apparatus for correcting spinal deformities and the method of using the apparatus. In each embodiment of Miskew, the rod which is employed has either a threaded surface or a surface including a plurality of adjustment stop surfaces (FIG. 25). This is different from the teachings of the present invention wherein rods with smooth surfaces are employed as well as other distinctions.
U S. Pat. No. 4,361,141 to Tanner discloses a scoliosis transverse traction assembly which acts as a tensioning device to maintain two spaced rods in position with respect to each other. The tensioning device includes a transverse threaded rod with a basket hook at one end and a transverse hook toward the other end. The position of the transverse hook is adjustable along the transverse rod. This is different from the turn-buckle-type coupler of the present invention.
U.S. Pat. No. 4,567,884 to Edwards discloses a spinal hook designed to be used with a spinal correction system, which system includes both threaded rods and rods with projecting annular surfaces (ratchets) thereon. The hooks of Edwards may be modified for use with the present invention by incorporating an open back and further adapting the hook to accept the locking sleeve of the present invention. However, the present invention is distinct from the teachings of Edwards.
U.S. Pat. No. 4,611,582 to Duff discloses a vertebral clamp designed to be used between two adjacent vertebrae through attachment to the laminae thereof. The clamp includes two clamp members, one for each vertebra and a threaded coupling member designed to be used to adjust the distance between the clamps to achieve the desired spacial relationship. In contrast with this teaching, the present invention includes mid-line clamps which may be used to fix the position of elongated smooth surfaced rods on the posterior spine.
U.S. Pat. No. 4,641,636 to Cotrel discloses a device for supporting the rachis which includes the use of both closed and open back hooks supported on a rod having a knurled surface defined in this patent as having "a multitude of aspirates 21, obtained for example by milling or turning." A screw member 25 is utilized to secure the hooks to the knurled rod. This is different from the teachings of the present invention wherein smooth surfaced rods are employed as well as other distinctions.
French Patent No. 2,151,475 to Cotrel discloses a spinal appliance designed to be attached between two greatly spaced points on a spinal column as best seen in FIG. 7 through the use of end hooks. This is different from the teachings of the present invention wherein a desired curvature of the spine may be obtained by pre-bending a pair of smooth surfaced rods and affixing a plurality of components and appliances thereto to achieve a separation between the rods, as well as a desired configuration of the spine.
French Patent No. 2,244,446 to Cotrel discloses a transverse threaded rod to maintain two spaced spinal rods (one a ratcheted rod and one a threaded rod) in spaced relation with respect to each other. This is different from the turnbuckle-type coupler assembly of the present invention. Other distinctions also exist including, for example, the use in the present invention of smooth surfaced rods.
Zimmer Publication titled "Edwards Spinal Fixation System", 1984, discloses a spinal system developed in conjunction with Dr. Charles C. Edwards, including rods, sleeves and hooks. The sleeves (also described by U.S. Pat. No. 4,369,769 to Edwards) act as spacers between the spinal rod and the spine. The Edwards Anatomic Hooks shown in this publication correspond to the above-mentioned U.S. Pat. No. 4,567,884 to Edwards.
Zimmer Publication titled "Interspinous Segmental Spinal Instrumentation: Surgical Technique", by Dr. Denis S. Drummond and James Keene, 1984, discloses instruments and appliances used in performing spinal surgery. The system utilizes a paired, button/wire implant in which wires are tied to various types of spinal rods. The present invention does not utilize such a button/wiring technique.
Zimmer Publication titled "KNODT Distraction-Fusion Instrumentation", 1980, discloses the use of hooks mounted on threaded shafts designed to separate adjacent vertebrae from one another by a predetermined distance. This is different from the teachings of the present invention which uses open-backed hooks as well as smooth surfaced rods.
Zimmer Publication titled "Luque Segmental Spinal Instrumentation Surgical Technique", 1980, discloses segmental spinal instrumentation developed in conjunction with Dr. Edwardo R. Luque. In the Luque system and technique, elongated rods are used along with twisted wiring to hold the smooth rods in the desired spaced relation. This is different from the teachings of the present invention which does not utilize such a wiring technique.
Zimmer Publication titled "Wisconsin Compression System", discloses the use of prior art, Harrington, Keene and Drummond systems. The Keene hook disclosed in U.S. Pat. No. 4,269,178, discussed above, is employed and the use of threaded rods as well as rods having consecutive projections (ratchets) thereon is disclosed. The teachings of the present invention are distinct from the teachings of this publication, as including the use of rods which are smooth surfaced and wherein split sleeve locking assemblies are used to hold the various components on the rods.
An article entitled "A Locking Hook Spinal Rod System For Stablization of Fracture-Dislocations," Jacobs et al, Clinical Orthopaedics and Related Research, No. 189, October 1984, pp. 168-177, discloses a spinal system which utilizes a locking cover to secure the lamina in the hook and meshing radial grooves to lock the contoured rod to the upper and lower hooks. This is different from the smooth rod, open back hook and locking sleeves of the present invention.